Authentication has been standardized in International Mobile Telecommunication 2000 (IMT-2000), which is a 3rd generation mobile communication scheme, for example, Wideband Code Division Multiple Access (WCDMA), and in Global System for Mobile Communications (GSM), which is one of 2nd generation mobile communication schemes and has compatibility with IMT-2000.
Authentication is realized by mounting, on a subscriber mobile station such as a mobile phone or a wireless terminal, a Universal Subscriber Identity Module (USIM) or a Subscriber Identity Module (SIM), which is a typical subscriber identity module issued by a network service provider or the like having a service contract with the subscriber of a mobile communication network. Authentication refers to mutual authentication required upon call origination and termination between the mobile communication network serviced by the network service provider or the like and a subscriber identity module (USIM or SIM).
In order for a mobile station to be provided with call service, a subscriber identity module is authenticated. A conventional procedure for authenticating a USIM using UMTS Authentication and key agreement (AKA) is performed in such a way that when the mobile station sends an authentication request message for the USIM to an authentication server via a mobile switching center such as Visitor Location Register (VLR) and Serving GPRS Support Node(SGSN), the authentication server transmits authentication vector(s) required to perform authentication to the mobile station, and the USIM performs authentication using a memory address, which relates to an index value used in the array scheme of the USIM, and a sequence number included in the authentication vector.
That is, when preset authentication conditions are satisfied using the sequence number of the memory address included in the authentication vector and the sequence number included in the authentication vector, it is determined that authentication has succeeded and then the sequence number of a relevant memory address is replaced with and stored as the sequence number included in the authentication vector, whereas when the preset authentication conditions are not satisfied, it is determined that authentication has failed.
In this case, when authentication has failed, the USIM transmits the maximum sequence number separately stored in memory and a memory address corresponding thereto, for example, 550[10], where 550 corresponds to the maximum sequence number and [10] corresponds to memory address, to the VLR/SGSN, and the VLR/SGSN sends an authentication failure message to the authentication server such as Home Environment (HE) or Home Location Register (HLR). Accordingly, the HE/HLR generates, for example, three authentication vectors, including sequence numbers generated based on the maximum sequence number and three consecutive memory addresses sequentially increased from the relevant memory address by 1, for example, A[11], B[12], and C[13], and transmits the authentication vectors to the VLR/SGSN. The VLR/SGSN transmits an authentication vector including A[11] to the relevant mobile station, and the mobile station performs re-authentication by comparing a sequence number stored in the memory address [11] included in the authentication vector with A.
The HE/HLR transmits the three authentication vectors to the VLR/SGSN, and then generates and stores three authentication vectors for subsequent memory addresses. For example, three authentication vectors respectively including D[14], E[15], and F[16] are generated and stored.
However, when the memory address [11] is impaired and re-authentication fails, a message including 550[10] which is the maximum sequence number [memory address] used in the failed authentication is sent to the VLR/SGSN. The VLR/SGSN transmits a network fail message to the mobile station in conformity with a standard procedure for re-authentication failure to allow the mobile station to again attempt to request authentication, and transfers only information about re-authentication failure to the HE/HLR. Upon re-authentication failure, the VLR/SGSN deletes all previously-stored authentication vectors.
When the mobile station, having received NetworkFail message from the VLR/SGSN, requests authentication again after several seconds in conformity with the standard, the VLR/SGSN requests an authentication vector from the HE/HLR because of the absence of the previously-stored authentication vector(s). The HE/HLR further transmits three authentication vectors including previously generated/stored D[14], E[15], and F[16] to the VLR/SGSN, and then the VLR/SGSN transmits the authentication vector including D[14] to the mobile station.
In this case, if the memory address [14] is also impaired, authentication fails again, and then the mobile station requests re-authentication from the VLR/SGSN by transmitting 550[10] which is the maximum sequence number [memory address] to the VLR/SGSN. As described above, since the authentication vectors for [11] and [14], at which memory addresses are impaired, are transmitted to the mobile station, the entire procedure including authentication failure, re-authentication failure, and an authentication request after several seconds is continuously repeated, and the failure of authentication is repeated, thus preventing call service from being provided to the mobile station.
In this way, in the conventional USIM authentication method, when an insignificant amount of damage is caused on USIM memory, and then sequence numbers are changed to an abnormal state, and authentication vectors including impaired memory addresses are received, the above procedure including authentication failure, re-authentication failure, and an authentication request is infinitely repeated. Therefore, in order to be provided with call service as a result of successful authentication, an existing USIM must be replaced with a USIM having non-damaged memory, thus incurring additional costs for the replacement of the USIM.